Method for manufacturing image sensor

ABSTRACT

Methods for forming an image sensor structure are provided. The method includes forming a light-sensing region in a substrate and forming a storage node adjacent to light-sensing region in the substrate. The method further includes forming a front side isolation structure partially surrounding an upper portion of the light-sensing region and forming a trench fully surrounding a bottom portion of the light-sensing region to expose a bottom surface of the front side isolations structure. The method further includes forming a backside isolation structure in the trench.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a Divisional application of U.S. patent applicationSer. No. 14/942,441, filed on Nov. 16, 2015, the entire of which isincorporated by reference herein.

BACKGROUND

Semiconductor integrated circuit devices are used in a variety ofelectronic applications, such as personal computers, cell phones,digital cameras, and other electronic equipment. Semiconductor devicesare typically fabricated by sequentially depositing insulating ordielectric layers, conductive layers, and semiconductor layers ofmaterial over a semiconductor substrate, and patterning the variousmaterial layers using lithography to form circuit components andelements thereon.

Over the past several decades, the semiconductor integrated circuitindustry has experienced rapid growth. Technological advances insemiconductor materials and design have produced increasingly smallerand more complex circuits. These material and design advances have beenmade possible as the technologies related to processing andmanufacturing have also undergone technical advances.

Many of the technological advances in semiconductors have occurred inthe field of image sensing. A backside illuminated (B SI) image sensoris one of the types of image sensors used in integrated circuits.However, although existing backside illuminated image sensors havegenerally been adequate for their intended purposes, as devicescaling-down continues, they have not been entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 1B is a pixel layout shown from the backside of the image sensorstructure in accordance with some embodiments.

FIG. 1C is a cross-sectional representation of the image sensorstructure shown along line A-A′ shown in FIG. 1A in accordance with someembodiments.

FIGS. 2A to 2E are cross-sectional representations of various stages offorming an image sensor structure in accordance with some embodiments.

FIGS. 3A to 3D are cross-sectional representations of various stages offorming an image sensor structure in accordance with some embodiments.

FIGS. 4A to 4B are cross-sectional representations of various stages offorming an image sensor structure in accordance with some embodiments.

FIG. 5 is a cross-sectional representation of an image sensor structure100 e in accordance with some embodiments.

FIG. 6A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 6B is a cross-sectional representation of the image sensorstructure shown along line B-B′ shown in FIG. 6A in accordance with someembodiments.

FIG. 7A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 7B is a cross-sectional representation of the image sensorstructure along line C-C′ in accordance with some embodiments.

FIGS. 8A and 8B are cross-sectional representations of image sensorstructures in accordance with some embodiments.

FIG. 9A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 9B is a cross-sectional representation of the image sensorstructure along line D-D′ in accordance with some embodiments.

FIG. 10 is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 11A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 11B is a representation of a possible electrical potential indifferent area of the image sensor structure in accordance with someembodiments.

FIG. 12A is a pixel layout shown from a front side of an image sensorstructure in accordance with some embodiments.

FIG. 12B is a cross-sectional representation of the image sensorstructure alone line E-E′ shown in FIG. 12A in accordance with someembodiments.

FIG. 12C is a representation of a possible electrical potential indifferent area of the image sensor structure in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,”“lower,” “above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments of an image sensor structure and methods for forming thesame are provided. The image sensor structure may be a backsideilluminated (BSI) image sensor and includes a front side isolationstructure and the backside isolation structure formed around itslight-sensing region. The front side isolation structure and thebackside isolation structure may prevent parasitic light from enteringthe neighboring storage node, so that the performance of the imagesensor structure may be improved.

FIG. 1A is a pixel layout shown from a front side of an image sensorstructure 100 a in accordance with some embodiments. FIG. 1B is a pixellayout shown from the backside of the image sensor structure 100 a inaccordance with some embodiments. FIG. 1C is a cross-sectionalrepresentation of the image sensor structure 100 a shown along line A-A′shown in FIG. 1A in accordance with some embodiments.

The image sensor structure 100 a includes a substrate 102, and thesubstrate 102 has a front side 104 and a backside 106, as shown in FIGS.1A to 1C in accordance with some embodiments. In some embodiments, thesubstrate 102 is a semiconductor substrate including silicon. Thesubstrate 102 may be a semiconductor wafer such as a silicon wafer.Alternatively or additionally, the substrate 102 may include elementarysemiconductor materials, compound semiconductor materials, and/or alloysemiconductor materials. Examples of the elementary semiconductormaterials may be, but are not limited to, crystal silicon,polycrystalline silicon, amorphous silicon, germanium, and/or diamond.Examples of the compound semiconductor materials may be, but are notlimited to, silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide. Examples of thealloy semiconductor materials may be, but are not limited to, SiGe,GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP.

A light-sensing region 108 is formed in the substrate 102 in accordancewith some embodiments. In some embodiments, the light-sensing region 108formed through the substrate 102, as shown in FIG. 1C. The light-sensingregion 108 may be configured to sense (detect) incident light. Forexample, the light-sensing region 108 may correspond to a specific rangeof wavelengths, such as red light, green light, or blue light. In someembodiments, the light-sensing region 108 includes a photodiodestructure.

The light-sensing region 108 may be formed by performing ionimplantation processes on the substrate 102. The ion implantationprocesses may include multiple implant processes, and various dopants,implant dosages, and implantation energies may be used. In anembodiment, the light-sensing region 108 includes dopants having anopposite doping polarity as those in the substrate 102.

The image sensor structure 100 a further includes a front side isolationstructure 110 and a backside isolation structure 112 formed around thelight-sensing region 108 in accordance with some embodiments. Morespecifically, the front side isolation structure 110 is formed at thefront side of the substrate 102, as shown in FIG. 1C. The front sideisolation structure 110 may prevent light cross-talk between neighboringpixels. In some embodiments, the front side isolation structure 110partially surrounds the upper portion of the light-sensing region 108,as shown in FIG. 1A. In some embodiments, the front side isolationstructure 110 has an opening region 114 at one side of the upper portionof the light-sensing region 108, so that a portion of the light-sensingregion 108 is not surrounded by the front side isolation structure 110.

The front side isolation structure 110 may be made of a material whichis capable of blocking light from passing through. In some embodiments,the front side isolation structure 110 is made of nitride or oxide, suchas silicon oxide or silicon nitride. In some embodiments, the front sideisolation structure 110 is an air gap. In some embodiments, the frontside isolation structure 110 has a width W₁ in a range from about 50 nmto about 0.3 μm. In some cases, the width W₁ of the front side isolationstructure 110 may be controlled not to be too large, so thelight-sensing region 108 may have a greater size. On the other hand, insome cases, the width W₁ of the front side isolation structure 110 maybe controlled not to be too thin, or the formation of the front sideisolation structure 110 may be challenging.

In some embodiments, the front side isolation structure 110 has a heightH₁ in a range from about 0.25 μm to about 1.5 μm. In some cases, theheight H₁ of the front side isolation structure 110 cannot be too large,or the opening region 114 of the front side isolation structure 110 mayalso be too large and the performance of the image sensor structure 100a may be undermined.

The backside isolation structure 112 is formed at the backside 106 ofthe substrate 102, as shown in FIG. 1C. In addition, unlike the frontside isolation structure 110, the backside isolation structure 112 fullysurrounds the bottom portion of the light-sensing region 108 inaccordance with some embodiments. In some embodiments, the backsideisolation structure 112 is in direct contact with the front sideisolation structure 110.

The backside isolation structure 112 may be made of a material which iscapable of blocking light from passing through. In some embodiments, thebackside isolation structure 112 is made of nitride or oxide, such assilicon oxide or silicon nitride. In some embodiments, the backsideisolation structure 112 is made of a metal, such as tungsten. In someembodiments, the front side isolation structure 110 and the backsideisolation structure 112 are made of different materials. In someembodiments, the front side isolation structure 110 is made of adielectric material and the backside isolation structure 223 is made ofmetal. The isolation structure made of metal may have good opticalisolating ability but tend to melt under high temperature. Therefore,the front side isolation structure 110 may be made of a dielectricmaterial, which can stand a relatively high temperature performed insubsequent manufacturing processes, while the backside isolationstructure 223 may be made of metal.

In some embodiments, the backside isolation structure 112 is made of hasa width W₂ in a range from about 50 nm to about 0.3 μm. Similarly, thewidth W₂ of the backside isolation structure 112 may be controlled, sothat the light-sensing region 108 will have a greater size but theformation of the backside isolation structure 112 will not be toochallenging. In some embodiments, the backside isolation structure 112has a height in a range from about 0.25 μm to about 3 μm. In some cases,the height H₂ of the backside isolation structure 112 cannot be toolarge, or the backside isolation structure 112 may touch the storagenode 118. In some embodiments, the light-sensing region 108 has a widthW₃ in a range from about 0.5 μm to about 5 μm.

A gate structure 116 is formed over the front side 104 of the substrate102, and a storage node 118 is formed adjacent to the gate structure116, as shown in FIGS. 1A and 1C in accordance with some embodiments.The gate structure 116 may be partially overlapped with thelight-sensing region 108. In some embodiments, the gate structure 116includes polysilicon. In some embodiments, the gate structure 116 is amulti-gate structure, such as a FinFET gate structure.

The storage node 118 is formed at the front side 104 of the substrate102 and is located at the side of the light-sensing region 108 that isnot completely surrounded by the front side isolation structure 110. Asshown in FIG. 1A, the storage node 118 is formed adjacent to the openingregion 114 of the front side isolation structure 110, so that thelight-sensing region 108 is not isolated from the storage node 118 bythe front side isolation structure 110.

The storage node 118 is formed so that the electrons induced in thelight-sensing region 108 can be transferred into the storage node 118and be further transferred into a read-out transistor. By using thestorage node 118, image acquisition of various pixels may be performed(e.g. start and stop) simultaneously. Therefore, the performance of theimage sensor structure 110 a may be improved. For example, globalshutter function can be enabled. In some embodiments, the storage node118 is formed by an implanting process.

The image sensor structure 100 a further includes a light shieldinglayer 120 formed over the backside 106 of the substrate 102, as shown inFIGS. 1B and 1C in accordance with some embodiments. The light shieldinglayer 120 is configured to block the light from directly entering thestorage node 118 from the backside 106 of the substrate 102. On theother hand, the light-sensing region 108 is not covered by the lightshielding layer 120, so that light can incident from the backside 106 ofsubstrate 102 and enter into the light-sensing region 108. In someembodiments, the light shielding layer 120 is made of a metal, such asaluminum or tungsten.

In addition, the image sensor structure 100 a further includes aninterlayer dielectric layer 130, an interconnect structure layer 132,and a supporting substrate 134 formed over the front side 104 of thesubstrate, as shown in FIG. 3B in accordance with some embodiments. Asshown in FIG. 1C, the gate structure 116 is covered by the interlayerdielectric layer 130. The interlayer dielectric layer 130 may includemultilayers made of multiple dielectric materials, such as siliconoxide, silicon nitride, silicon oxynitride, and/or other applicablelow-k dielectric materials. The interlayer dielectric layer 130 may beformed by chemical vapor deposition (CVD), physical vapor deposition,(PVD), atomic layer deposition (ALD), spin-on coating, or otherapplicable processes.

The interconnect structure layer 132 is formed over interlayerdielectric layer 130 and may include numbers of conductive featuresformed in a dielectric layer. In some embodiments, the dielectric layeris inter-metal dielectric (IMD) layer. In some embodiments, thedielectric layer includes multilayers made of multiple dielectricmaterials, such as silicon oxide, silicon nitride, silicon oxynitride,phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), or otherapplicable low-k dielectric materials. The dielectric layer may beformed by a chemical vapor deposition (CVD), physical vapor deposition,(PVD), atomic layer deposition (ALD), spin-on coating, or otherapplicable processes.

The conductive features may include vertical interconnects, such as viasand contacts, and/or horizontal interconnects, such as conductive lines.In some embodiments, the conductive features are made of conductivematerials, such as aluminum, aluminum alloy, copper, copper alloy,titanium, titanium nitride, tungsten, polysilicon, or metal silicide.

In addition, the image sensor structure 100 a also includes anantireflective layer 136, a color filter layer 138, and a microlenslayer 140 formed over the backside 106 of the substrate 102, as shown inFIG. 1C in accordance with some embodiments. In some embodiments, theantireflective layer 136 is made of silicon carbide nitride, siliconoxide, or the like. After antireflective layer 136 is formed, apassivation layer, such as a silicon nitride layer or a siliconoxynitride layer, may be formed over the antireflective layer 136.

The color filter layer 138 may include more than one color filter. Thecolor filters may be aligned with the light-sensing regions 108 formedin the substrate 102. The color filters may be made of a dye-based (orpigment-based) polymer for filtering out a specific frequency band oflight. In addition, the microlens layer 140 disposed on the color filterlayer 138 may include more than one microlens. The microlenses in themicrolens layer 140 may be aligned with the color filters in the colorfilter layer 138.

As shown in FIG. 1C, an incident light 142 may enter the substrate 102from its backside 106 in accordance with some embodiments. Morespecifically, the incident light 142 may pass through the microlenslayer 140, the color filter layer 138, and the antireflective layer 136and enter into the light-sensing region 108 from the backside 106 of thesubstrate 102. Afterwards, the electrons induced in the light-sensingregion 108 may be transferred to the storage node 118 through theopening region 114 of the front side isolation structure 110. Inaddition, since the incident light is blocked by the light shieldinglayer 120, the backside isolation structure 112, and the front sideisolation structure 110, the incident light 142 will not directly reachthe storage node 118. Therefore, the risk of the storage node 118 beinginterfered by parasitic light may be reduced. Therefore, the performanceof the image sensor structure 100 a may be improved.

It should be noted the image sensor structure 100 a has been simplifiedfor better understanding the concept of the disclosure. For example, theimage sensor may include additional elements, such as reset transistors,floating diffusion, source follower transistor, row select transistor,capacitors, or the like, although they are not shown in FIGS. 1A to 1C.In addition, the number of light-sensing regions formed in the imagesensor structure 100 a may vary, and the scope of the disclosure is notintended to be limiting.

The front side isolation structure and the backside isolation structuredescribed above may be formed using various methods, and the scope ofthe disclosure is not intended to be limiting. FIGS. 2A to 2E arecross-sectional representations of various stages of forming an imagesensor structure 100 b in accordance with some embodiments. The imagesensor structure 100 b may be similar to, or the same as, the previouslydescribed image sensor structure 100 a. Therefore, the materials andprocesses used to form the image sensor structure 100 b that are similarto, or the same as, those used to form the image sensor structure 100 aare not repeated herein.

As shown in FIG. 2A, the light-sensing region 108, a front sideisolation structure 110 b, and the storage node 118 are formed from thefront side 104 of the substrate 102 in accordance with some embodiments.The gate structure 116 is formed over the front side 104 of thesubstrate 102. As described previously, the front side isolationstructure 110 b is formed around the upper portion of the light-sensingregion 108 but having the opening region 114 at one side of thelight-sensing region 108. Accordingly, the light-sensing region 108 isnot completely enclosed by the front side isolation structure 110 b, andthe electrons can be transferred from the light-sensing region 108 tothe storage node 118 through the opening region 114.

In some embodiments, the front side isolation structure 110 b may beformed by etching the substrate 102 from the front side of the substrate102 to form a trench, and filling the trench with an isolating material.

Next, the interlayer dielectric layer 130, the interconnect structurelayer 132, and the supporting substrate 134 are formed over the frontside 104 of the substrate 102, and a polishing process may be performedon the backside 106 of the substrate 102, as shown in FIG. 2B inaccordance with some embodiments. The polishing process may be performedon the backside 106 of the substrate until the light-sensing region 108is exposed from the backside 106 of the substrate. It should be notedthat additional elements may be formed in the interlayer dielectriclayer 130, the interconnect structure layer 132, and the supportingsubstrate 134, although they are not shown in FIG. 2B.

Afterwards, a trench 135 b may be formed from the backside 106 of thesubstrate 102, as shown in FIG. 2C in accordance with some embodiments.The trench 135 b is formed around the bottom portion of thelight-sensing region 108. After the trench 135 b is formed, the backsideisolation structure 112 b is formed in the trench 135 b so that thebottom portion of the light-sensing region 108 is surrounded by thebackside isolation structure 112 b.

After the backside isolation structure 112 b is formed, the lightshielding layer 120, the antireflective layer 136, the color filterlayer 138, and the microlens layer 140 are formed over the backside 106of the substrate 102 to form the image sensor structure 100 b.

FIGS. 3A to 3D are cross-sectional representations of various stages offorming an image sensor structure 100 c in accordance with someembodiments. The image sensor structure 100 c may be similar to, or thesame as, the previously described image sensor structure 100 a.Therefore, the materials and processes used to form the image sensorstructure 100 c that are similar to, or the same as, those used to formthe image sensor structure 100 a are not repeated herein.

As shown in FIG. 3A, the light-sensing region 108 is formed in thesubstrate 102, and the storage node 118 is formed at one side of thelight-sensing region 108 in accordance with some embodiments. Inaddition, the gate structure 116, the interlayer dielectric layer 130,the interconnect structure layer 132, and the supporting substrate 134are formed over the front side 104 of the substrate in accordance withsome embodiments. Next, a first trench 135 c is formed from the backside106 of the substrate 102, as shown in FIG. 3B in accordance with someembodiments. In addition, the first trench 135 c is formed around thelight-sensing region 108 with an opening region 114 c at one side of thelight-sensing region 108.

After the first trench 135 c is formed, a second trench 135 c′ is formedfrom the backside 106 of the substrate 102, as shown in FIG. 3C inaccordance with some embodiments. More specifically, a portion of thesubstrate 102 is etched from the backside 106 of the opening region 114c to form the second trench 135 c′. However, the second trench 135 c′does not pass through the substrate 102.

Next, the first trench 135 c and the second trench 135 c′ are filledwith an isolating material to form a front side isolation structure 110c and a backside isolation structure 112 c, as shown in FIG. 3C inaccordance with some embodiments. In some embodiments, the front sideisolation structure 110 c and the backside isolation structure 112 c aremade of the same material, and there is no real interface between them.After the front side isolation structure 110 c and the backsideisolation structure 112 c are formed, the light shielding layer 120, theantireflective layer 136, the color filter layer 138, and the microlenslayer 140 are formed over the backside 106 of the substrate 102 to formthe image sensor structure 100 c.

FIGS. 4A to 4B are cross-sectional representations of various stages offorming an image sensor structure 100 d in accordance with someembodiments. The image sensor structure 100 c may be similar to, or thesame as, the image sensor structure 100 a described previous. Therefore,the materials and processes used to form the image sensor structure 100d that are similar to, or the same as, those used to form the imagesensor structure 100 a are not repeated herein.

As shown in FIG. 4A, a first substrate 102 d and a second substrate 102d′ are received in accordance with some embodiments. The first substrate102 d includes a first light-sensing region 108 d formed in the firstsubstrate 102, a front side isolation structure 110 d formed around thelight-sensing region 108 d, and the storage node 118 formed in the firstsubstrate 102 d in accordance with some embodiments. As shown in FIG.4A, the front side isolation structure 110 d has an opening region 114 dand the storage node 118 is formed next to the opening region 114 d. Inaddition, the gate structure 116, the interlayer dielectric layer 130,the interconnect structure layer 132, and the supporting substrate 134are formed over the first substrate 102 d.

In addition, the second substrate 102 d′ includes a second light-sensingregion 108 d′ and a backside isolation structure 112 d formed around thesecond light-sensing region 108 d′. Furthermore, the light shieldinglayer 120, the antireflective layer 136, the color filter layer 138, andthe microlens layer 140 are formed over the backside of the secondsubstrate 102 d′.

Next, the first substrate 102 d and the second substrate 102 d′ arebonded together to form the image sensor structure 100 d, as shown inFIG. 4B in accordance with some embodiments. In some embodiments, thefirst light-sensing region 108 d is aligned with the secondlight-sensing region 108 d′, and the front side isolation structure 110d is aligned with the backside isolation structure 112 d.

FIG. 5 is a cross-sectional representation of an image sensor structure100 e in accordance with some embodiments. The image sensor structure100 e is similar to, or the same as, the image sensor structuresdescribed previously, such as the image sensor structure 100 a, exceptthat its front side isolation structure and backside isolation structureare not connected with each other. Materials and processes used to formthe image sensor structure 100 b may be similar to, or the same as,those described previously and are not repeated herein.

More specifically, the image sensor structure 100 e also includes thesubstrate 102 having the front side 104 and the backside 106 and thelight-sensing region 108 formed in the substrate 102. In addition, afront side isolation structure 110 e is formed at the front side 104 andpartially surrounds the upper portion of the image sensing region 108. Abackside isolation structure 112 e is formed at the backside 106 of thesubstrate 102 and fully surrounds the bottom portion of thelight-sensing region 108. The gate structure 116 is formed on the frontside 104 of the substrate, and the storage node 118 is formed adjacentto the gate structure 116. Interlayer dielectric layer 130, theinterconnect structure layer 132, and the supporting substrate 134 areformed over the front side 104 of the substrate 102, and theantireflective layer 136, the color filter layer 138, and the microlenslayer 140 are formed over the backside 106 of the substrate 102. Asshown in FIG. 5, the front side isolation structure 110 e is notconnected with the backside isolation structure 112 e.

FIG. 6A is a pixel layout shown from a front side of an image sensorstructure 100 f in accordance with some embodiments. FIG. 6B is across-sectional representation of the image sensor structure 100 f shownalong line B-B′ shown in FIG. 6A in accordance with some embodiments.Some materials and processes used to form the image sensor structure 100f may be similar to, or the same as, those used to formed the imagesensor structures described previously and are not repeated herein.

Similar to the image sensor structure 100 a, the image sensor structure100 c includes the substrate 102, the front side isolation structure110, the backside isolation structure 112, the gate structure 116, thestorage node 118, the interlayer dielectric layer 130, the interconnectstructure layer 132, the supporting substrate 134, the light shieldinglayer 120, the antireflective layer 136, the color filter layer 138, andthe microlens layer 140, as shown in FIGS. 6A and 6B in accordance withsome embodiments. In addition, the image sensor structure 100 f includesa light-sensing region 108 f, which has a smaller upper portion and alarger bottom portion, as shown in FIG. 6B in accordance with someembodiments.

In addition, a gate structure 122 is formed over the front side 104 ofthe substrate 102, and a drain structure 124 is formed adjacent to thegate structure 122, as shown in FIG. 6A in accordance with someembodiments. The gate structure 122 and the drain structure 124 may beseen as a lateral overflow transistor formed over the front side 104 ofthe substrate 102. The lateral overflow transistor may be configured totransfer surplus light out from the light-sensing region 108 f. In someembodiments, the gate structure 122 is partially overlapped with thelight-sensing region 108 f, but the drain structure 124 is not in directcontact with the light-sensing region 108 f. As described above, thelight-sensing region 108 f may have a smaller upper portion, so that thelight-sensing region 108 f will not touch the drain structure 124. Insome embodiments, the gate structure 122 is a polysilicon gate structureor a metal gate structure. In some embodiments, the drain structure 124is formed by implanting processes.

In some embodiments, a gate structure 126 is formed at a side of thestorage node 118, and a floating node 128 is formed adjacent to the gatestructure 126, as shown in FIG. 6A in accordance with some embodiments.The floating node 128 may be configured to connect with a read-outamplifier. In some embodiments, the gate structure 126 is a polysilicongate structure or a metal gate structure. In some embodiments, thefloating node 128 is formed by implanting processes.

FIG. 7A is a pixel layout shown from a front side of an image sensorstructure 100 g in accordance with some embodiments. FIG. 7B is across-sectional representation of the image sensor structure 100 g alongline C-C′ in accordance with some embodiments. The image sensorstructure 100 g may be similar to the image sensor structure 100 adescribed previously, except that a cap layer 701 g is formed in theimage sensor structure 100 g. Elements, materials, and processesdescribed previously may not be repeated herein.

More specifically, the image sensor structure 100 g includes thesubstrate 102, the front side isolation structure 110, the backsideisolation structure 112, the light-sensing region 108, the gatestructure 116, the storage node 118, the interlayer dielectric layer130, the interconnect structure layer 132, the supporting substrate 134,the light shielding layer 120, the antireflective layer 136, the colorfilter layer 138, and the microlens layer 140, as shown in FIGS. 7A and7B in accordance with some embodiments.

In addition, the image sensor structure 100 g includes a cap layer 701 gformed in the interlayer dielectric layer 130. As shown in FIG. 7A, thecap layer 701 g is formed over the front side 104 of the substrate 102,so that the light-sensing region 108 is covered by the cap layer 701 g.The formation of the cap layer 701 g is configured to prevent theincident light from entering the storage node 118 through the layersformed over the light-sensing region 108 (e.g. the interlayer dielectriclayer 130) due to light diffraction or reflection. In some embodiments,the cap layer 701 a is a flat layer formed over the light-sensing region108 and is not in direct contact with the gate structure 116, as shownin FIG. 7B. In some embodiments, the cap layer 701 g is made of a metal,such as tungsten, aluminum, or copper.

FIGS. 8A and 8B are cross-sectional representations of image sensorstructures 100 h and 100 i in accordance with some embodiments. Theimage sensor structure 100 h is similar to the image sensor structure100 g, except that the position of a cap layer 701 h formed in the imagesensor structure 100 h is different from that of the cap layer 701 g, asshown in FIG. 8A in accordance with some embodiments. In someembodiments, a portion of the cap layer 701 h is directly formed on thelight-sensing region 108 and therefore is in direct contact with the topsurface of the light-sensing region 108. In some embodiments, the caplayer 701 h has a step-like shape formed along the sidewall and the topsurface of the gate structure 116, but the cap layer 701 h is not indirect contact with the gate structure 116. Since the cap layer 701 h isdirectly formed on the light-sensing region 108, the parasitic light canbe reduced.

The image sensor structure 100 i is similar to the image sensorstructure 100 g, except that a cap layer 701 i in the image sensorstructure 100 i is formed in the interconnect structure layer 132instead of interlayer dielectric layer 130, as shown in FIG. 8B inaccordance with some embodiments. As shown in FIG. 8B, the cap layer 701i is formed in the interconnect structure layer 132. In someembodiments, the cap layer 701 i is also used as a metal line in theinterconnect structure layer 132. That is, other conductive featuresformed in the interconnect structure layer 132 are electricallyconnected to the cap layer 701 i in accordance with some embodiments.

FIG. 9A is a pixel layout shown from a front side of an image sensorstructure 100 j in accordance with some embodiments. FIG. 9B is across-sectional representation of the image sensor structure 100 j alongline D-D′ in accordance with some embodiments. The image sensorstructure 100 j may be similar to, or the same as, the previouslydescribed image sensor structure 100 g, except that a blocking structure803 is formed in the image sensor structure 100 j. Elements, materials,and processes described previously may not be repeated herein.

As shown in FIG. 9B, the image sensor structure 100 j includes theblocking structure 803 which is configured to prevent the incident lightfrom entering the storage node formed nearby (e.g. a storage node 118′formed in the neighboring pixel) in accordance with some embodiments. Insome embodiments, the blocking structure 803 is in direct contact withthe cap layer 701 g and the front side isolation structure 110. In someembodiments, a portion of the blocking structure 803 extends into thefront side isolation structure 110. In some embodiments, the blockingstructure 803 and the cap layer 701 g are made of the same material. Insome embodiments, the blocking structure 803, the cap layer 701 g, andthe front side isolation structure 110 are made of the same material. Insome embodiments, the blocking structure 803 is made of a metal, such astungsten, aluminum, or copper.

FIG. 10 is a pixel layout shown from a front side of an image sensorstructure 100 k in accordance with some embodiments. Some portions ofimage sensor structure 100 k may be similar to, or the same as, those ofthe previously described image sensor structure 100 f and may not berepeated herein. In addition, the features shown in FIGS. 1A to 9Bdescribed previously may also be formed in the image sensor structure100 k, although they may not be shown in FIG. 10.

The image sensor structure 100 k includes a storage node 118 k formedover the front side of the substrate 102. In addition, the storage node118 k is located at a position where the storage node 118 k is separatedfrom the light-sensing region 108 by the front side isolation structure110. That is, instead of being positioned next to the opening region 114of the front side isolation structure 110 (as the storage node 118described previously), the storage node 118 k is formed at the portionstaggered from the opening region 114. In some embodiments, the storagenode 118 k is placed at the diagonal position from the light-sensingregion 108.

As shown in FIG. 10, the light-sensing region 108, the opening region114 of the front side isolation structure 110, and the storage node 118k are not aligned in a straight line in the layout from the top view.Accordingly, although the front side isolation structure 110 also hasthe opening region 114, the risk of parasitic light entering the storagenode 118 k through the opening region 114 may be reduced. However, sincestorage node 118 k is not positioned next to the opening region 114, agate structure 1005 is formed over the front side of the substrate 102to connect the light-sensing region 108 and the storage node 118 k. Thegate structure 1005 can be seen as a transfer gate structure. Theelectrons induced in the light-sensing region 108 can be transferred tothe storage node 118 k through the gate structure 1005.

In some embodiments, the storage node 118 k is surrounded by additionalisolation structure 110 k. In addition, the isolation structure 110 kalso has an opening region 114 k, so that a portion of the storage node118 k is not surrounded by the isolation structure 114 k. As shown inFIG. 10, one end of the gate structure 1005 overlaps with the openingregion 114 of the front side isolation structure 110, and the other endof the gate structure 1005 overlaps with the opening region 114 k of theisolation structure 110 k. The materials and processes used to form theisolation structure 110 k may be similar to, or the same as, those usedto form the previously described front side isolation structure 110. Inaddition, it should be noted that, although the storage node 118 k isformed in a position different from that of the storage node 118described previously, the materials and processes used to form thestorage node 118 k may be similar to, or the same as, those used to formthe previously described storage node 118 and are not repeated herein.

FIG. 11A is a pixel layout shown from a front side of an image sensorstructure 100 l in accordance with some embodiments. Some portions ofimage sensor structure 100 l may be similar to, or the same as, those ofthe previously described image sensor structure 100 k and may not berepeated herein. In addition, the features described previously may alsobe formed in the image sensor structure 100 k, although they may not beshown in FIG. 10.

Similar to the image sensor structure 100 k, the image sensor structure100 l also includes a storage node 118 l formed at the front side of thesubstrate 102, as shown in FIG. 11A in accordance with some embodiments.In addition, the storage node 118 l is located at a position where thestorage node 118 l is separated from the light-sensing region 108 by thefront side isolation structure 110. The position of the storage node 118l and the formation of it may be similar to, or the same as, those ofthe storage node 118 k described above.

As described previously, since the light-sensing region 108, the openingregion 114 of the front side isolation structure 110, and the storagenode 118 l are not aligned in a straight line in the layout, the risk ofparasitic light entering the storage node 118 l through the openingregion 114 may be reduced. In addition, the storage node 118 l issurrounded by an additional isolation structure 110 l, and the isolationstructure 110 l also has an opening region 114 l. In some embodiments, agate structure 1107 is formed over the opening region 114 of the frontside isolation structure 110, and a gate structure 1109 is formed overthe opening region 114 l of the isolation structure 110 l.

As shown in FIG. 11A, the image sensor structure 100 l includes anintermediate region 111 l. The gate structure 1107 is formed at one sideof the intermediate region 111 l, and the gate structure 1109 is formedat the other region of the intermediate region 111 l. In someembodiments, the intermediate region 111 l is surrounded by an isolationstructure 110 l′.

In some embodiments, an intermediate transistor structure is formed atanother side of the intermediate region 111 l. In some embodiments, theintermediate transistor structure includes an intermediate gatestructure 1113 and an intermediate node 1115 formed adjacent to theintermediate gate structure 113. When the intermediate transistorstructure is turned on, unwanted charges coming to the intermediateregion 111 l may be directed away by the intermediate transistorstructure. On the other hand, when the intermediate transistor structureis turned off, the signals induced by the light-sensing region 108 (e.g.the integrated charged) may be directed to the storage node 118 l. Itshould be noted that, although the intermediate transistor is shown inFIG. 11A, it is not used in some other embodiments. That is, theformation of the intermediate transistor may be optional according toits applications.

FIG. 11B is a representation of a possible electrical potential indifferent area of the image sensor structure 100 l in accordance withsome embodiments. As shown in FIG. 11B, the y-axis represents theelectrical potential in each area. The electrical potential in thelight-sensing region 108 is greater than the electrical potential in theintermediate region 111 l, and the electrical potential in theintermediate region 111 l is greater than the electrical potential inthe storage node 118 l. In addition, the electrical potential in thestorage node 118 l is greater than the floating node 128. Furthermore,the gate structures 1107, 114 l, and 126 may be used to control theelectrons passing through. In some embodiments, the electrical potentialof these regions may be adjusted by controlling the dopant'sconcentration in each region.

FIG. 12A is a pixel layout shown from a front side of an image sensorstructure 100 m in accordance with some embodiments. FIG. 12B is across-sectional representation of the image sensor structure 100 m aloneline E-E′ shown in FIG. 12A in accordance with some embodiments. Someportions of image sensor structure 100 m may be similar to, or the sameas, those of the previously described image sensor structure 100 k andmay not be repeated herein.

Similar to the image sensor structure 100 k, the image sensor structure100 m also includes a storage node 118 m formed at the front side of thesubstrate 102, as shown in FIG. 12A in accordance with some embodiments.In addition, the storage node 118 m is located at a position where thestorage node 118 m is separated from the light-sensing region 108 by thefront side isolation structure 110. The position of the storage node 118m and the formation of it may be similar to, or the same as, those ofthe storage node 118 k described above. In some embodiments, a gatestructure 1209 is formed over an opening region 114 m of the isolationstructure 110 m.

As described previously, since the light-sensing region 108, the openingregion 114 of the front side isolation structure 110, and the storagenode 118 m are not aligned in a straight line in the layout, the risk ofparasitic light entering the storage node 118 m through the openingregion 114 may be reduced. In addition, the storage node 118 m issurrounded by an additional isolation structure 110 l, and the isolationstructure 110 m also has an opening region 114 m.

Furthermore, the image sensor structure 100 m further includes anadditional photodiode region 108 m, as shown in FIGS. 12A and 12B inaccordance with some embodiments. The additional photodiode region 108 mis formed next to the opening region 114 of the front side isolationstructure 110, so that the electrons induced in the light-sensing region108 can be transferred into the additional photodiode region 108 m. Insome embodiments, the light-sensing region 108 also includes aphotodiode region, and the two photodiode regions are formed at theopposite sides of the opening region 114 of the front side isolationstructure 110.

In addition, the image sensor structure 100 m includes a light shieldinglayer 120 m, which is similar to, or the same as, the light shieldinglayer 120 described previously. As shown in FIG. 12B, the light-sensingregion 108 is not covered by the light shielding layer 120 m, andtherefore the incident light can enter the light-sensing region 108 fromthe backside 106 of the substrate 102. On the other hand, the additionalphotodiode region 108 m is covered by the light shielding layer 120 m,and therefore the incident light cannot directly enter the additionalphotodiode region 108 m from the backside 106 of the substrate 102.However, since the light-sensing region 108 and the additionalphotodiode region 108 m are not isolated from each other at the openingregion 114, the electrons in the light-sensing region 108 can be storedin the additional photodiode region 108 m. Therefore, the full-wellcapacity of the image sensor structure 100 m can be increased.

In addition, a lateral overflow transistor structure, including a gatestructure 122 m and a drain structure 124 m, is formed at a side of theadditional photodiode region 108 m. The function and processes forforming the gate structure 122 m and the drain structure 124 m may besimilar to, or the same as, those of the gate structure 122 and thedrain structure 124 described previously and are not repeated herein.

FIG. 12C is a representation of a possible electrical potential indifferent area of the image sensor structure 100 m in accordance withsome embodiments. Similar to FIG. 11B, the y-axis in FIG. 12C representsthe electrical potential in each area. The electrical potential in thelight-sensing region 108 is greater than the electrical potential in theadditional photodiode region 108 m, and the electrical potential in theadditional photodiode region 108 m is greater than the electricalpotential in the storage node 118 m. In addition, the electricalpotential in the storage node 118 m is greater than the floating node128. Furthermore, the conductive structures 114 m and 126 may be used tocontrol the electrons passing through. In some embodiments, theelectrical potential of these regions may be adjusted by controlling thedopant's concentration in each region.

It should be noted that the gate structures described above may bemulti-gate structures, such that the number of the gate structuresformed in a given area can be increased. Therefore, the size of theimage sensor structures may be minimized.

The image sensor structures described previously, including image sensorstructures 100 a to 100 m, may be BSI image sensor structures. Inaddition, global shutter structures may also be applied in the BSI imagesensor structures. As described previously, storage nodes, such as thestorage node 118, are formed on the front side 104 of the substrate 102and are positioned near the light-sensing region 108. Accordingly, theelectrons induced in the light-sensing region 108 can be transferredinto the storage node 118, and therefore the image acquisition can beperformed simultaneously. Accordingly, the performance of the imagesensor structure can be improved.

In addition, when the storage node 118 is formed in the front side 104of the substrate, the light shielding layer 120, the front sideisolation structure 110, and the backside isolation structure 112 arealso formed to prevent the incident light from directly entering thestorage node 118. However, the light-sensing region 108 is notcompletely surrounded by the front side isolation structure 110, so thatthe electrons can be transferred into the storage node 118 through theopening region 114.

Furthermore, in some embodiments, the cap layer 701 g is formed toprevent the light from entering the storage node 118 due to diffractionor reflection in the layers positioned over the light-sensing region108. In some embodiments, the blocking structure 803 is also formed toblock the light from entering the neighboring storage node, such as thestorage node 118′. Accordingly, the risk of parasitic light entering thestorage node may be reduced further.

In some embodiments, the storage node, such as the storage node 118 k,118 l, or 118 k, is formed at a position away from the opening 114 ofthe front side isolation structure 110. By misaligning the openingregion 114, which exposes the light-sensing region 108, and the storagenode, parasitic light may be prevented. In addition, additional gatestructures, such as gate structures 1005, 1107, 1109, and 1209, may beused, so that the electrons induced in the light-sensing region 108 canstill be transferred into the storage node. In some embodiments, theadditional photodiode region 108 m is formed next to the light-sensingregion 108, and the full-well capacity of the image sensor structure canbe increased.

Embodiments of image sensor structures and methods for manufacturing thesame are provided. The image sensor structure includes a light-sensingregion formed in a substrate, and a storage node formed near thelight-sensing region. In addition, the image sensor structure furtherincludes a front side isolation structure formed in the front side ofthe substrate, and a backside isolation structure formed in the backsideof the substrate. The upper portion of the light-sensing region ispartially surrounded by the front side isolation structure, and thebottom portion of the light-sensing region is fully surrounded by thebackside isolation structure. The front side isolation structure and thebackside isolation structure can prevent light from directly enteringthe storage node, while the electrons induced in the light-sensingregion can be transferred to the storage node through an opening regionof the front side isolation structure. Therefore, the performance of theimage sensor structure can be improved.

In some embodiments, a method for manufacturing an image sensorstructure is provided. The method includes forming a light-sensingregion in a substrate and forming a storage node adjacent tolight-sensing region in the substrate. The method further includesforming a front side isolation structure partially surrounding an upperportion of the light-sensing region and forming a trench fullysurrounding a bottom portion of the light-sensing region to expose abottom surface of the front side isolations structure. The methodfurther includes forming a backside isolation structure in the trench.

In some embodiments, a method for manufacturing an image sensorstructure is provided. The method includes forming a light-sensingregion in a substrate and forming a storage node adjacent to thelight-sensing region. The method further includes forming a first trenchpartially surrounding an upper portion of the light-sensing region inthe substrate and forming a front side isolation structure in the firsttrench. The method further includes forming a second trench surroundinga bottom portion of the light-sensing region and partially overlaps withthe storage node in the substrate and forming a backside isolation inthe second trench.

In some embodiments, a method for manufacturing an image sensorstructure is provided. The method for manufacturing the image sensorstructure includes forming a light-sensing region in a substrate andforming a first trench from a front side of the substrate. In addition,the first trench partially surrounds the light-sensing region. Themethod for manufacturing the image sensor structure further includesfilling a first material in the first trench to form a front sideisolation structure and forming a second trench from a backside of thesubstrate. In addition, the second trench fully surrounds thelight-sensing region. The method for manufacturing the image sensorstructure further includes filling a second material in the secondtrench to form a backside isolation structure. In addition, the firstmaterial is different from the second material and is in direct contactwith the second material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing an image sensorstructure, comprising: forming a light-sensing region in a substrate;forming a storage node adjacent to light-sensing region in thesubstrate; forming a front side isolation structure partiallysurrounding an upper portion of the light-sensing region; forming atrench fully surrounding a bottom portion of the light-sensing region toexpose a bottom surface of the front side isolations structure; andforming a backside isolation structure in the trench.
 2. The method formanufacturing an image sensor structure as claimed in claim 1, whereinthe front side isolation structure is made of a first material and thebackside isolation structure is made of a second material different fromthe first material.
 3. The method for manufacturing an image sensorstructure as claimed in claim 2, wherein the first material is adielectric material and the second material is metal.
 4. The method formanufacturing an image sensor structure as claimed in claim 1, furthercomprising: forming a gate structure over a front side of the substrate,wherein the gate structure partially overlaps with the light sensingregion and the front side isolation structure.
 5. The method formanufacturing an image sensor structure as claimed in claim 1, whereinthe storage node partially overlaps with the backside isolationstructure.
 6. The method for manufacturing an image sensor structure asclaimed in claim 1, further comprising: forming an interconnectstructure layer over a frond side of the substrate; and forming a lightshielding layer over a backside of the substrate, wherein the lightshielding layer overlaps with the front side isolation structure and thebackside isolation structure.
 7. A method for manufacturing an imagesensor structure, comprising: forming a light-sensing region in asubstrate; forming a storage node adjacent to the light-sensing region;forming a first trench partially surrounding an upper portion of thelight- sensing region in the substrate; forming a front side isolationstructure in the first trench; forming a second trench surrounding abottom portion of the light-sensing region and partially overlaps withthe storage node in the substrate; and forming a backside isolation inthe second trench.
 8. The method for manufacturing an image sensorstructure as claimed in claim 7, wherein the front side isolationstructure is formed before the second trench is formed.
 9. The methodfor manufacturing an image sensor structure as claimed in claim 7,wherein the front side isolation structure and the backside isolationstructure are made of different materials.
 10. The method formanufacturing an image sensor structure as claimed in claim 9, whereinthe front side isolation structure is in direct contact with thebackside isolation structure.
 11. The method for manufacturing an imagesensor structure as claimed in claim 7, wherein the substrate comprisesa first wafer and a second wafer bonded to the first wafer, and thefront side isolation structure is formed in the first wafer and thebackside isolation structure is formed in the second wafer.
 12. Themethod for manufacturing an image sensor structure as claimed in claim7, wherein a portion of the light sensing region and the storage nodeare not separated by the first isolation structure.
 13. The method formanufacturing an image sensor structure as claimed in claim 7, whereinthe first isolation structure is separated from the second isolationstructure by a portion of the substrate.
 14. A method for manufacturingan image sensor structure, comprising: forming a light-sensing region ina substrate; forming a first trench from a front side of the substrate,wherein the first trench partially surrounds the light-sensing region;filling a first material in the first trench to form a front sideisolation structure; forming a second trench from a backside of thesubstrate, wherein the second trench fully surrounds the light-sensingregion; and filling a second material in the second trench to form abackside isolation structure, wherein the first material is differentfrom the second material and is in direct contact with the secondmaterial.
 15. The method for manufacturing an image sensor structure asclaimed in claim 14, wherein the first material is a dielectric materialand the second material is metal.
 16. The method for manufacturing animage sensor structure as claimed in claim 14, wherein a bottom surfaceof the front side isolation structure is exposed by the second trench.17. The method for manufacturing an image sensor structure as claimed inclaim 14, further comprising: forming a gate structure over the frontside of the substrate, wherein the gate structure overlaps with thebackside isolation structure.
 18. The method for manufacturing an imagesensor structure as claimed in claim 17, further comprising: forming aninterconnect structure layer over the frond side of the substrate; andforming a light shielding layer over the backside of the substrate. 19.The method for manufacturing an image sensor structure as claimed inclaim 18, wherein the light shielding layer overlaps with the front sideisolation structure and the backside isolation structure.
 20. The methodfor manufacturing an image sensor structure as claimed in claim 19,wherein a portion of the light sensing region and the storage node arenot separated by the first isolation structure.